MICROBRACHIUS DICKI. 105 



History. — The first mention of the little Asterolepid which forms the type of 

 this genus is in a paper by the late Mr. C. W. Peach, " On Fossil Fishes of the 

 Old Red Sandstone of Caithness and Sutherland," in the ' Proceedings ' of the 

 meeting of the British Association held at Dundee in 18G7. After remarking that 

 up to 1863 not a vestige of Pterichthys had been found in Caithness or Sutherland, 

 he stated that he found this exceedingly small species at John O'Groats in the 

 former county. He gave, however, no description of it beyond saying that it had 

 small spined arms, but remarks that " if a new species, the author intends to call 

 it after his late valued friend, Robert Dick." 



Peach's specimens having come into the possession of the Edinburgh Museum, 

 I gave in 1888 a brief description of the species which was unquestionably new 

 to science. And on account of the want of a tail capable of preservation, coupled 

 with the peculiar articulation of the anterior median dorsal plate, I proposed to 

 make it the type of a new genus — namely Microbrachius. 



Microbeachius Dicki, Traquair. Plate XXII, figs. 5 — 8. 



1867. Pterichthys Dicki, G. W. Peach. Kep. Brit. Assoc, for 1867 (1868) ; 



Trails. Sect., p. 72 (name only). 

 1888. Microbeachius Dicki, Traquair. G-eol. Mag. [3], vol. v, p. 510, and Ann. 



Mag. Nat. Hist. [6], vol. ii, p. 502, 

 pi. xviii, figs. 7 and 8. 

 1891. Microbrachium Dicki, A. S. Woodward. Cat. Foss. Fishes Brit. Mus., 



pt. ii, p. 223. 



Description. — As there is only one species of the genus known, no specific 

 diagnosis is necessary. 



It is quite a small creature, varying in length from f to 1^ inch. The shape 

 of the carapace recalls that of Bothriolepis in being evidently depressed — broad 

 dorsally, but narrow on the flat ventral aspect. Figs. 5 and 6 on PI. XXII 

 represent two specimens in which the dorsal plates are seen from the internal 

 aspect, and, though crushed quite flat, give a good idea of the general form of the 

 back of the creature, the arrangement of the plates of which as visible from 

 within is also seen in the appended text-figure 56. 



The head is large, being almost as long as the dorsal portion of the carapace ; 

 its posterior contour is angulated so as to fit into the corresponding wide angular 

 excavation of the anterior margin of the last named part. None of the specimens 

 show any cranial osteological details, save some faint indications of the position of 

 the orbit, and of the outline of the premedian plate. 



As already mentioned, the dorsal aspect of the carapace is broad like that of 



